【作者】 何方；

【导师】 徐桂英；

【作者基本信息】 山东大学 ， 胶体与界面化学， 2011， 博士

【摘要】 胆盐是一种重要的生物表面活性剂,主要存在于脊椎动物中,可用作增溶剂或乳化剂以促进日常饮食中摄入的油脂的吸收,在医学中还可以治疗胆结石。胆盐类物质一般都包括两部分,其中凹陷的a面是由带有极性羟基的类固醇骨架构成,而凸出的p面则是由亚甲基组成的。这种排布方式造就了胆盐的独特性质,与传统的直链型表面活性剂有很大不同。因此,关于胆盐的聚集行为的研究具有非常重要的意义。关于添加剂对传统表面活性剂聚集行为影响的研究报道有很多,比如CTAB、SDS和Triton X-100等,而对于胆盐类表面活性剂的研究较少。在本论文中,我们选择脱氧胆酸钠(NaDC)为研究对象,采用表面张力、界面扩张流变、计算机模拟和荧光光谱的方法研究了三种碱性氨基酸(L-赖氨酸(L-Lys).L-精氨酸(L-Arg)和L-组氨酸(L-His))对NaDC在气/液界面上和水溶液中的聚集行为的影响,并考察了混合体系对非诺贝特的增溶作用；采用体相流变和透射电子显微镜的方法研究了无机钠盐对NaDC凝胶的流变行为的影响,以期为了解此类体系在生理环境中的聚集行为提供信息,为开拓胆盐类生物表面活性剂在不同领域的应用提供基础数据和理论依据。论文主要包括五部分内容：论文的第一部分概述了胆盐表面活性剂的特性,并综述了胆盐的聚集行为以及添加剂对NaDC聚集行为的影响的研究进展。论文的第二部分采用表面张力、界面扩张流变和计算机模拟的方法研究了三种碱性氨基酸对NaDC在气/液界面上的聚集行为的影响。结果表明,氨基酸的加入可以降低NaDC在水溶液中的临界聚集浓度(cac),NaDC之cac值的对数与氨基酸浓度的对数呈直线关系,但直线的斜率较低；随着NaDC浓度增加,体系的绝对模量呈现先上升后下降的趋势,加入氨基酸后绝对模量的峰值增大。三种氨基酸中L-Lys对NaDC的cac和界面流变性的影响最大,据此推测,NaDC和氨基酸之间的静电作用和疏水作用是主要驱动力。论文的第三部分采用荧光光谱法研究了氨基峻对NaDC在水溶液中的聚集行为的影响。结果表明,NaDC在水溶液中的聚集是二级缔合过程,NaDC分子间通过疏水作用形成初级聚集体,而后在氢键和疏水作用的共同驱动下形成了一级聚集体。氨基酸的加入可以降低NaDC在水溶液中的微极性和cac值,而聚集数显著增加。L-Lys对微极性、cac和聚集数的影响最大,而L-Arg和L-His对三种参数的影响较小。据此推测,NaDC和氨基酸之间的静电作用、疏水作用和氢键都是NaDC聚集体生长的重要驱动力。从氨基酸的pKa值和疏水指数来看,L-Lys对NaDC聚集行为的影响最大,而NaDC与三种氨基酸之间的氢键大小的差别不大。因此,氨基酸与NaDC相互作用的强弱主要依赖于它们之间的静电和疏水作用。论文的第四部分采用紫外光谱法研究了三种氨基酸对NaDC增溶非诺贝特效果的影响。结果表明,NaDC浓度越大,体系的温度越高,非诺贝特在NaDC溶液中的表观溶解度越大。在固定NaDC浓度时,可以根据公式计算得到摩尔溶解焓ΔsolHm。非诺贝特从不含NaDC的缓冲溶液转移至NaDC缓冲溶液过程的迁移焓ΔtrH和迁移熵TΔtrS都是负值,并且随着NaDC浓度的增加而降低,说明NaDC对非诺贝特的增溶过程是焓驱动过程。加入氨基酸后,NaDC增溶能力加强,且随着氨基酸浓度增加,增溶能力逐渐提高。氨基酸的结构不同,对其增溶能力的影响也不同,三种氨基酸与NaDC的混合体系对非诺贝特的增溶能力排序如下：L-Lys>L-Arg≈L-His。结合第三章的研究结果,可以推测,静电作用、疏水作用和氢键三种作用力共同控制NaDC与氨基酸混合体系对非诺贝特的增溶过程,而体系的微极性、临界聚集浓度和聚集数的变化对NaDC的增溶作用具有很大的影响。论文的第五部分采用体相流变和透射电子显微镜的方法对比研究了无机钠盐对NaDC凝胶的流变行为的影响。结果表明,钠盐的存在可以使得NaDC聚集体沿着一个方向生长,最终形成交错的网络结构,而其它无机盐(如KCl、MaCl2、CaCl2和AICl3)则不能诱导NaDC凝胶的形成。随着NaDC浓度增加,凝胶的三个特征参数(剪切粘度、弹性模量和松弛时间)都随之增大,说明NaDC分子数目的增大有利于形成稳定的网络结构。随着盐浓度增加,三个参数都呈现先逐渐增加后缓慢减小的趋势,说明较低盐浓度有利于网络结构的形成,而盐含量较高时将破坏网络结构,并且在盐析作用影响下,使得NaDC分子自聚集而从溶液中析出。在这三种钠盐中,NaCl对NaDC凝胶流变行为的影响最为显著(?)所形成凝胶的网络结构最稳定,强度最大,而NaBr和NaI对其影响相对较小这个排列顺序与感胶离子序一致,离子半径越小,水化作用越强,与水分子之间的作用越强,越有利于NaDC分子的自聚集。更多还原

【Abstract】 Bile salts are important biosurfactants, which exist in the living bodies of vertebrates, and often act as solubilizing or emulsifying agents for absorption of dietary lipids, or as gallstone solubilizing agents in clinical medicine. All of them possess a rigid steroid backbone having polar hydroxyl groups on the concave a-face and methylene groups on the convexβ-face. This arrangement creates unique physiochemical properties for such a class of molecules, being different from those of conventional surfactants with a linear hydrocarbon chain. It is of great importance that the aggregation behavior of bile salts should be investigated.To our knowledge, the effect of additives on the aggregation behavior of the traditional surfactant, such as CTAB, SDS and Triton X-100, has been paid much more attention. However, details on the interactions between bile salts and additives have not been investigated deeply up to now. In this thesis, sodium deoxycholate (NaDC) is employed to study the effect of additives on its aggregation behavior. Surface tension, dilational viscoelasticity, molecular dynamic simulation and steady-state fluorescence spectra of pyrene of NaDC aqueous solution are investigated in the absence and presence of three kinds of alkaline amino acids, namely L-Lysine (L-Lys), L-Arginine (L-Arg) and L-Histidine (L-His), in order to study the aggregation behaviors of NaDC at the air/water surface and in aqueous solution. The effect of amino acids on the solubility of fenofibrate in NaDC solution was studied using UV-vis spectrum method. The rheological properties of NaDC hydrogel as a function of concentration of NaDC and salts were investigeted by rheological measurements. This research may open an avenue to gain a better knowledge about the behavior of such systems in the biological environment. This thesis is divided into five parts.In the first section, the properties of bile salt, the study progress on the aggregation behaviors of bile salts and the effect of additives on the aggregation bahavior of NaDC are summarized. In the second section, the aggregation behaviors of NaDC at air/water surface were investigated via surface tension and oscillating bubble measurements in the absence and presence of three alkaline amino acids. The results of surface tension show that NaDC has lower ability in reducing surface tension of water, because NaDC molecules orient at the surface with an oblique direction and tend to aggregate together, which is approved by the molecular dynamic simulation. L-Lys is the most efficient one among three amino acids in reducing critical aggregation concentration (cac) of NaDC in aqueous solution. The influence of amino acids on the dilational rheological properties of NaDC was studied using the drop shape analysis method in the frequency range from 0.02 to 0.5 Hz. The results reveal that the absolute modulus passes through a maximum value with increasing NaDC concentration. The addition of amino acids increases the absolute modulus of NaDC solution and the maximum value is observed at much lower concentration. From the perspective of structures of amino acids, the performance of L-Arg is similar to that of L-His, and both of them bring out smaller effect on the absolute modulus than that of L-Lys. From the above results, it may be presumed that electrostatic and hydrophobic effects are important impetus during the interaction between amino acids and NaDC at air/water surface. Hydrogen bonding is so ubiquitous in the system that the difference of hydrogen bonding between NaDC and amino acid is ignored.In the third section, the influence of three alkaline amino acids on the aggregation behaviors of NaDC in phosphate buffer (pH=7.0) was studied at 25℃. The fluorescence probe technique of pyrene was employed to determine accurately the cac, polarity of microenvironment and aggregation numbers for NaDC aggregate. The added amino acids can effectively reduce the cac values and micropolarity of NaDC, indicating that it is easier for NaDC to aggregate together and lie compactly in the presence of amino acids. Meanwhile, the aggregation numbers of NaDC are increased evidently, meaning that more NaDC molecules connect together to form stable aggregates. It is worth mentioning that the performance of L-Arg is similar to that of L-His, and both of them bring out smaller effect on the above parameters than L-Lys. In view of this, it may be inferred that both electrostatic and hydrophobic interaction are responsible for the interaction between NaDC and amino acids in aqueous solution.In the fourth section, the ability of NaDC to solubilize fenofibrate in the absence and presence of amino acids was studied using UV-vis spectrum method. The solubility of fenofibrate is increased with increasing NaDC’s concentration and temperature. At fixed NaDC concentration, the enthalpy of solution,ΔSolHm can be calculated from the slopes of the Van’t Hoff plots. The characteristics of transfer enthalpy and entropy for fenofibrate from buffer to NaDC solution reveal that,ΔtrH and TΔtrS decrease in the negative region with increasing concentration of NaDC. In the negative region, drug dissolution is enthalpy favorable and entropy unfavorable, and enthalpy effect is overcomes the entropy effect. The solubility of fenofibrate is increased with increasing concentration of amino acids. From the perspective of structures of amino acids, the performance of L-Arg is similar to that of L-His, and both of them bring out smaller effect on the solubility of fenofibrate than that of L-Lys. From the above results, it may be presumed that electrostatic, hydrophobic effects and hydrogen bonding are important impetus during the solubilization of fenofobrate in NaDC/amino acid solution. Moreover, the micropolarity, cac values and aggregation numbers of NaDC in the absence and presence of amino acids can be employed to interpret the solubilization process.In the fifth section, the rheological behavior of NaDC hydrogel was investigated in the presence of sodium halide, including NaCl, NaBr and NaI. The added sodium salts is favorable to the growth of NaDC aggregates in a direction and thus the entangled network is formed due to the interaction between NaDC and sodium halide. However, other inorganic salts, such as KCl, MaCl2, CaCl2 and AlCl3 are impossible to induce the formation of NaDC hydrogel. With increasing concentration of NaDC, three parameters, including the viscosity, elastic modulus and retardation time, increase remarkably. It can be inferred that the increasing NaDC molecules are favorable to the formation of network.These parameters first incerase and then decrease slowly with increasing concentration of sodium salts. At a low salt content, the added salt can effectively screen the elactrostatic interaction among hydrophilic groups of NaDC and thus factor the formation of network. Addition of more salt makes excessive aggregation and eventually the gelator molecules start to escape from the gel network by precipitation. Among three kinds of sodium halide, NaCl is most effective in improving the strength of NaDC hydrogel, while Nal bring out smaller effect than those of NaCl and NaBr. This sequence is in agreement with the lyotropic series, indicating that the ion with samller radius has stronger hydration effect and thus the interaction between it and water is much stronger. Undoubtedly, the NaDC molecules are easy to aggregate in the presence of smaller ions.更多还原